Conventional automotive vehicles typically include a mechanical brake pedal that is connected to a brake lever or arm. The motion of the brake arm in turn actuates a braking mechanism, such as a disc brake or a drum brake, to thereby slow and/or stop the vehicle. The rate of deceleration imparted to the vehicle depends on the amount of force applied to actuate or depress the brake pedal and on the travel position of the brake pedal within or along the range of motion of the brake pedal. Conventional hydraulic braking systems in particular are powered by a supply of pressurized brake fluid delivered from a master cylinder. Such a mechanical, fluid-powered braking system responds relatively quickly and accurately to a force applied to the brake pedal through the pedal's entire range of motion, providing what could be described as a “normal” or conventional brake pedal “feel”.
By way of contrast, a by-wire or electronic braking system (EBS) is often used in electric vehicles, as well as in hybrid vehicles which are alternately and selectively powered by an internal combustion engine or fuel cell and one or more electric motor/generators. Using an EBS, the braking command or input applied as a force to a brake pedal by an operator of the vehicle is converted by an encoder device into an electrical braking signal. This electrical braking signal, also known as a braking torque request, is then rapidly transmitted or communicated to the point of application, where one or more actuators operate in response to the signal to slow or stop the vehicle. Braking torque in a vehicle having an EBS may be applied directly using an electro-hydraulic and/or an electromechanical braking mechanism to apply pressure to brake calipers to slow the vehicle, or more commonly by applying an opposing torque to an individual electronic braking unit positioned in proximity to each wheel, and/or to a transmission output shaft, thereby slowing the vehicle in a precisely controlled manner.
In an electric or a hybrid vehicle, the brake pedal is isolated from the actual point of application of the braking torque, and therefore is attached to one or more pedal sensors which detect or measure the pressure on the brake pedal and/or the position of the brake pedal and convert the measurements into the aforementioned transmittable electrical signal. A controller has preprogrammed braking system logic for translating the electrical signal into a corresponding braking torque request. Typically, such braking logic includes one or more accessible braking torque look-up tables containing specific braking torque requests corresponding to the detected brake pedal forces for a particular sensor type.
Certain pressure or force sensors may have less than optimal resolution, particularly under low force conditions, such as might occur when very light pressure is applied to a brake pedal. Using a brake pedal force sensor alone under these conditions may result in an error or variance in the braking torque request that is communicated to the EBS when compared to the vehicle operator's intended braking force. While sensors used to measure a brake pedal's relative position within or along its range of motion, i.e. the brake pedal travel, generally have better resolution at lower pressure ranges, mechanical hysteresis within the braking system may also potentially lead to errors or variances in the resulting applied braking torque request in the event of an attempted direct or immediate switch between sensors during low pressure applications.